The smallest cells with the simplest type of internal organization lack a nucleus — an enclosed region inside the cell where the DNA is separated from the rest of the cell by a double membrane. Instead, the DNA in these cells is concentrated in an area inside the cell called the nucleoid. Such cells are named prokaryotes (“pro” means before, “karyon” means nucleus).

Anthony Van Leeuwenhoek (1632-1723), Dutch merchant was fond of making magnifying lenses and with his homemade microscope saw “more life in a scraped human tooth than people in the whole kingdom” (1683)

 

 

 

Prokaryotic cells are small, consisting of cytoplasm surroundedby a plasma membrane and encased within a rigid cell wall, with no distinct interior compartments. Bacteria are very important in the economy of living organisms. They harvest light in photosynthesis, break down dead organisms and recycle their components, cause disease, and are involved in many important industrial processes.

SHAPES OF BACTERIA

There are many different types of bacteria. One way of classifying them is by shape. There are three basic shapes

• Spherical: Bacteria shaped like a ball are called cocci. Examples include the streptococcus group, responsible for “step throat.”
• Rod-shaped: These are known as bacilli. Some rod-shaped bacteria are curved. These are known as vibrio. Examples of rod-shaped bacteria include Bacillus anthracis, or anthrax.
• Spiral: These are known as spirilla. If their coil is very tight they are known as spirochetes. Examples: Leptospirosis, Lyme disease, syphilis are caused by bacteria of this shape.

STRUCTURE

Capsule: A layer found on the outside of the cell wall in some bacteria.
Cell wall: A layer that is made of a polymer called peptidoglycan. The cell wall gives the bacteria its shape. It is located outside the plasma membrane . The cell wall is thicker in some bacteria, called Gram positive bacteria.
Plasma membrane: Found within the cell wall, this generates energy and transports chemicals. The membrane is permeable, which means that substances can pass through it.
Cytoplasm: A gelatinous substance inside the plasma membrane that contains genetic material and ribosomes.
DNA: This contains all the genetic instructions used in the development and function of the bacterium. It is located inside the cytoplasm.
Ribosomes: This is where proteins are made, or synthesized. Ribosomes are complex particles made up of RNA-rich granules.
Flagellum: This is used for movement, to propel some types of bacteria. There are some bacteria that can have more than one.
Pili: These hair-like appendages on the outside of the cell allow it to stick to surfaces and transfer genetic material to other cells. This can contribute to the spread of illness in humans.

FEEDING

Bacteria feed in different ways.

Heterotrophic bacteria, get their energy through consuming organic carbon. Most absorb dead organic material, such as decomposing flesh. Some of these parasitic bacteria kill their host, while others help them.

Autotrophic bacteria make their own food, either through either:

• photosynthesis, using sunlight, water and carbon dioxide, or chemosynthesis, using carbon dioxide, water, and chemicals such as ammonia, nitrogen, sulfur, ferum.

Bacteria that use photosynthesis are called photoautotrophs. Some types, for example cyanobacteria, produce oxygen. These probably played a vital role in creating the oxygen in the earth’s atmosphere. Others, such as heliobacteria, do not produce oxygen.

Those that use chemosynthesis are known as chemoautotrophs. These bacteria are commonly found in ocean vents.

WHERE DO BACTERIA LIVE?

Bacteria can be found in soil, water, plants, animals, radioactive waste, deep in the earth’s crust, arctic ice and glaciers, and hot springs. There are bacteria in the stratosphere, between 6 and 30 miles up in the atmosphere, and in the ocean depths, down to 32,800 feet or 10,000 meters deep.

Aerobes, or aerobic bacteria, can only grow where there is oxygen. Some types can cause problems for the human environment, such as corrosion, fouling, problems with water clarity, and bad smells.

Anaerobes, or anaerobic bacteria, can only grow where there is no oxygen. In humans, this is mostly in the gastrointestinal tract. They can also cause gas, gangrene, tetanus, botulism, and most dental infections.

Facultative anaerobes, or facultative anaerobic bacteria, can live either with or without oxygen, but they prefer environments where there is oxygen. They are mostly found in soil, water, vegetation and some normal flora of humans and animals. Examples – Salmonella.

Mesophiles, or mesophilic bacteria, are the bacteria responsible for most human infections. They thrive in moderate temperatures, around 37°C. This is the temperature of the human body.

Examples include Listeria monocytogenes, Pesudomonas maltophilia, Thiobacillus novellus, Staphylococcus aureus, Streptococcus pyrogenes, Streptococcus pneumoniae, Escherichia coli, and Clostridium kluyveri.

The human intestinal flora, or gut microbiome, contains beneficial mesophilic bacteria, such as dietary Lactobacillus acidophilus.

Extremophiles, or extremophilic bacteria, can withstand conditions considered too extreme for most life forms.

Thermophiles can live in high temperatures, up to 75 to 80°C, and hyperthermophiles can surivive in temperatures up to 113°C.

Deep in the ocean, bacteria live in total darkness by thermal vents, where both temperature and pressure are high. They make their own food by oxidizing sulfur that comes from deep inside the earth.

Other extremophiles include:

• halophiles, found only in a salty environment
• acidophiles, some of which live in environments as acidic as pH 0
• alkaliphiles, living in alkiline environments up to pH 10.5
• psychrophiles, found in cold temperatures, for example, in glaciers

Extremophiles can survive where no other organism can.

REPRODUCE

Bacteria may reproduce and change using the following methods:

Binary fission: An asexual form of reproduction, in which a cell continues to grow until a new cell wall grows through the center, forming two cells. These separate, making two cells with the same genetic material.

 

 

 

Transfer of genetic material: Cells acquire new genetic material through processes known as conjugation, transformation, or transduction. These processes can make bacteria stronger and more able to resist threats, such as antibiotic medication.

 

 

FORMATION OF SPORES

When some types of bacteria are low on resources, they can form spores. Spores hold the organism’s DNA material and contain the enzymes needed for germination. They are very resistant to environmental stresses. The spores can remain inactive for centuries, until the right conditions occur. Then they can reactivate and become bacteria.

Spores can survive through periods of environmental stress, including ultraviolet (UV) and gamma radiation, desiccation, starvation, chemical exposure, and extremes of temperature.

Spores in microbes serve to carry adverse conditions. They are formed from the inside of the contents of the cell. At the same time, a new, denser shell is formed around the spore. Spores can tolerate very low temperatures (down to -273 ° C) and very high temperatures. Spores of some microbes do not die when boiling water.

VALUE IN HUMAN LIFE

Fermentation processes are of great importance; this is mainly the name for the decomposition of carbohydrates. In particular, as a result of fermentation, it turns into kefir and other products; ensiling of fodder is also fermentation. Fermentation also occurs in the human intestine. Without the appropriate bacteria (eg E. coli), the intestines cannot function normally. Rotting, useful in nature, undesirable in everyday life (for example, spoilage of meat products). Fermentation is not always useful (for example, sour milk). To prevent food spoilage, they are salted, dried, canned, kept in refrigerators. Thus, they reduce the activity of bacteria. But sauerkraut is stored longer than fresh, due to the activity of lactic acid bacteria, which make it impossible for bacteria to decay.

 

USE OF SAPROPHITE BACTERIA

 

DISEASE-CAUSING BACTERIA

bacterial pneumonia, dysentery, salmonellosis, botulism as well as:

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